If for H4 visa stamp in home country then check the other threads it has been posted many times.
If for H4 extension of status from BCIS in US then:
Fill up the form I-539
H1 Approval Notice copy and copy of valid I-94 (front and Back)
H4 holder copy of valid I-94 ((front and Back)
Passport pages of H4 holder that have DOB, Name, Photo and all pages that have previous H4 visa, US entry stamps
H1 holders recent 2-3 pay stubs.
Copy of marriage certificate
Fee Check for $ 140 to BCIS
List all the documents on cover letter and mark the envelop out side “ Extension of H4 status) and mail to BCIS service center with correct address with return reciept
All the documents should be sent to BCIS before H4 holders I-94 expire read the instruction from Form I-539
